This investigation will study substantia nigra (SN) - induced alterations of: (1) cortical input to hypoglossal (Xll) motoneurons; (2) cortical input to neurons in the spinal trigeminal nucleus (SPV), in untreated cats, as well as cats treated acutely and chronically with neuroleptic agents. Both intra-and extracellular recordings from neurons in the Xll and SPV nuclei will be employed. In addition, the neuropharmacology of neurons in both the Xll and SPV nuclei will be studied in the treated and non-treated animals by means of the iontophoretic administration of dopamine agonists, antagonists, and other putative neurotransmitters. It the hypothesis that drug-induced oral facial dyskinesia is due to the development of a dopamine receptor hypersensitivity to dopamine, such hypersentsitivity may be demonstrated in cranial nerve nuclei (Xll and SPV) which play a crucial role in regulating oral-facial movement.